Our long-term goal is to develop preventative treatments for inflammatory bone loss as manifested in pathologies such as prosthetic loosening (septic or aseptic) and periodontal infection. M-SCF and RANKL are two essential pro-osteoclastogenic and pro-inflammatory cytokines that stimulate macrophages to form osteoclasts. Our preliminary data showed that MAP Kinase/ ERK1/2 is an important signal transducer responsible for RANKL and MCSF gene expression. The objective of this A1 proposal is to define the role of ERK signaling in osteoblast-mediated innate immunity in response to biomaterials by conducting in vivo and in vitro mechanistic experiments. Our central hypothesis that ERK signaling mediates bone innate immunity in response to biomaterials by regulating pro-osteoclastogenic cytokine expression and inflammatory osteolysis. We will conduct mechanistic studies using a clinically relevant rodent femoral implant model and osteoblast-specific ERK1/2 dysfunction (ERKdef mice). The use of ERK pathway inhibitors is clinically feasible in that such inhibitors are currently being used in clinical trials for treatment of cancers with heightened levels of ERK activation. The advantage of ERK targeting lies in the fact that ERK is a central signaling station where upstream and downstream inflammatory signals cross. Specific Aims are as follows; Specific Aim 1. To determine whether ERK mediates inflammatory bone loss by regulating M-CSF and RANKL gene expression in osteoblasts. We will conduct experiments on mechanistic cellular signaling pathways responsible for M-CSF and RANKL expression after stimulation with LPS and UHMWPE in vitro and in vivo using osteoblast specific ERKdef mice. Specific Aim 2. To determine the therapeutic effect of ERK signal blockage in a clinically relevant femoral osteolysis model. We will examine the effect of pharmacologic inhibition of ERK signaling on UHMWPE or LPS-induced osteolysis in rat femora by quantitative microCT and biomechanical pullout testing. Specific Aim 3. To examine how ERK 1/2 signaling blockage affects interactions between osteoblasts and osteoclasts in the context of biomaterials and implant contaminants such as bacterial toxin. We will examine osteoclastogenesis by co-culturing ERKdef mice cells and macrophages. We will measure osteoclastogenesis, cytokine expression and bone resorption in the presence and absence of ERK signaling blockage. Specific Aim 4. To determine the specific mechanism by which ERK and NF:B P50 co-regulate M-CSF gene induction in osteoblasts in response to particulate biomaterials and LPS. While the ERK/ATF4/RANKL pathway is well established, there is a knowledge gap in the transcriptional regulation of M-CSF. We will examine the cooperative regulation of MCSF gene induction by ERK and NFkb We expect to verify a novel concept of competent osteoblastic innate immunity and define the role of ERK signaling in inflammatory bone loss in response to biomaterials and related toxins. PUBLIC HEALTH RELEVANCE: The clinical rationale underlying this study is that we can prevent or treat clinically important inflammatory bone loss by targeting an ERK-mediated inflammatory pathway with the use of specific topical or systemic inhibitors.